This invention relates generally to the control of an actuator in a hydraulic system and more particularly to a hydraulic system with an actuator having independent meter-in meter-out control which permits the actuator to regenerate flow from one end of the actuator to the other end and/or to permit interconnection of the ends of the actuator to provide a float function.
Hydraulic systems having independent control of fluid into and out of an actuator is generally known, such as that illustrated in FIGS. 6 and 12 of U.S. Pat. No. 4,662,601 which issued May 5, 1987. In these known systems, a separate poppet or check type of valve has been used to control the flow into and out of each end of the actuator. The above noted patent also provides a float mode of operation. Various types of poppet valves and various control schemes have been set forth to control the opening and closing of the valving element within the poppet valve. One such poppet valve and control scheme is set forth in U.S. Pat. No. 5,421,545 which issued Jun. 6, 1995 and is assigned to Caterpillar Inc. The poppet valve of ""545 is effective to proportionally control the flow therethrough. However, when used in a fluid circuit that desires to provide selective flow regeneration from the one end of an actuator to the other end of the actuator or a float function, the control scheme becomes complicated. It is known to provide flow regeneration in fluid circuits using a poppet valve arrangement between a multiple position control valve and the actuator. However, when using a multi-position control valve, the ability to independently control the flow into and out of the respective ends of the actuator is limited. It is desirable to provide a fluid circuit that has the ability to independently control the fluid flow into and out of an actuator while also providing the ability to regenerate flow from the one end to the other end.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a fluid circuit is provided and has a reservoir, a source of pressurized fluid connected to the reservoir, and an actuator having first and second inlet/outlet ports is selectively connected to the source of pressurized fluid and the reservoir. The fluid circuit is operative to selectively provide regenerative fluid flow from first inlet/outlet port of the actuator to the second inlet/outlet port thereof. The fluid circuit comprises a first poppet valve arrangement disposed between the source of pressurized fluid and the first inlet/outlet port of the actuator. The first poppet valve arrangement is operative to proportionally control the flow of fluid from the source of pressurized fluid to the first inlet/outlet port of the actuator. A second poppet valve arrangement is disposed between the first inlet/outlet port of the actuator and the reservoir and is operative to proportionally control the flow of fluid from the first inlet/outlet port of the actuator to the reservoir. A third poppet valve arrangement is disposed between the source of pressurized fluid and the second inlet/outlet port of the actuator and operative to proportionally control the flow of fluid from the second inlet/outlet port of the actuator to the reservoir. A control valve arrangement is connected to the source of pressurized fluid in parallel with the first poppet valve arrangement and is disposed between the source of pressurized fluid and the second inlet/outlet port of the actuator. The control valve arrangement is operative to proportionally control the flow of fluid from the source of pressurized fluid to the second inlet/outlet port of the actuator and to control the regenerative flow of fluid from the second inlet/outlet port of the actuator to the first inlet/outlet port of the actuator. A controller is provided and is operative in response to an input command to control the fluid flow into and out of the respective ends of the actuator.